The processing of fiber in all applications, from weaving, stitching, fabric manufacturing to composites processing, requires the dispensing of the fiber, or bundles of fibers, from a source such as a doff, spool, or other consolidation grouping. Between the dispensing and the processing, it is most often necessary for the fibers, or bundle of fibers, to be tensioned to process correctly. Appropriate tension in the fiber, or bundles of fiber, will result in processing that is desired and acceptable. The method of creating tension in fiber or fiber bundles has been mechanical, and has performed via methods involving bars, springs, weights, brakes, dancers, and a multitude of frictional devices (all of these referred to generally herein as “mechanical systems”). All of these mechanical methods have limitations, and require human interface for adjustment to properly process the fiber or fiber bundles.
For example, frequently a set of bars are used to serpentine the fibers in a repeated pattern over/under bars. This frictional impairment to a free-flowing fiber results in tension. The mechanical setting of these bars in spaced relation to each other determines the resulting tension.
Other existing systems use Ultra-High Molecular Weight (UHMW) plastic blocks that have eyelets formed (ceramic eyelets can also be used). Through a series of eyelets or holes in the UHMW block, one can serpentine the fiber back-and-forth until enough friction causes the desired resulting tension. Other systems have mechanical brake and friction systems to back-tension the spools of fiber to cause resistance in the pull-off of fiber. Besides being variable due to wear and diameter of spools, these methods have proven unreliable.
With some operations running hundreds and even thousands of fibers or fiber bundles in parallel, it is very important to have a close tolerance on the tension of each fiber or fiber bundle. Technologies of the past using mechanical tensioning systems can be vastly improved.
There is also a need to have very accurate tension, at high levels, in some composites processing of both thermoset and thermoplastic composites. These requirements impose a need to have consistent, wear resistant tension that is extremely accurate and easy to program with a CNC approach.